(a) Technical Field of the Invention
The present invention relates to power transmission structure, and in particular, to a power transmission structure for a dual blade shaft of a circular saw. A first and a second transmission shaft surround a dual-layered transmission roller so that the circular saw blade on the driving shaft and the blade on the driven shaft rotate in opposite direction.
(b) Description of the Prior Art
A circular saw for a saw mill includes a single blade shaft and a dual blade shaft. The power transmission structure of the dual blade shaft of a conventional circular saw is shown in FIGS. 1 and 2. The platform of the circular saw has a height adjustable seat body 10 having a driving element 11. A belt is used to drive the driving shaft 12 and the driving shaft 12 on different end of the saw blade has a driving roller 16. One side of the seat body 10 is a driven shaft 20 having a pre-cut blade 21 on a straight line position with the circular saw blade 15. The other end of the driven shaft 20 is provided with a driven roller 22. An elastic transmission belt 23 is positioned between the driving roller 16 and the driven roller 22. In order to let the circular saw blade 15 and the pre-cut blade 21 rotate in opposite direction, the elastic transmission belt 23 surrounds the driving roller 16 and the driven roller in a “8” shape.
In application, there are drawbacks found in this conventional structure. As shown in FIGS. 2, 3 and 4, due to the different in the thickness of wood, for excellent sawing of wood, the height of the saw blade 15 has to be adjusted depending on the thickness of the wood. Thus, the position of the seat body 10 has to be changed frequently. Thus, the gap between the driving roller shaft 12 and the driven shaft 20 is changed so as to maintain the transmission effectiveness. In other words, elastic transmission belt 33 is needed in order to achieve his objective.
However, the cost of the transmission belt 23 is high and therefore, the cost of production is increased. Further, the elastic transmission belt 23 does not resist to high temperature and it is fragile, and therefore, the cost of maintenance is high. In addition, the belt 23 is easily fragile and the accuracy of transmission will be affected.